Shielding coating for selective metallization

ABSTRACT

Shielding coatings are applied to polymer substrates for selective metallization of the substrates. The shielding coatings include a primer component and a hydrophobic top coat. The primer is first applied to the polymer substrate followed by application of the top coat component. The shielding coating is then selectively etched to form an outline of a desired current pattern. A catalyst is applied to the patterned polymer substrate followed by electroless metal plating in the etched portions. The portions of the polymer substrate which contain the shielding coating inhibit electroless metal plating. The primers contain polyamines and the top coat contains hydrophobic alky organic compounds.

FIELD OF THE INVENTION

The present invention is directed to shielding coatings for selectivemetallization of polymer substrates relating to molded interconnectdevices. More specifically the present invention is directed toshielding coatings for selective metallization of polymer substrates formolded interconnect devices where the shielding coating acts as abarrier layer to subsequent catalyst and electroless metal plating.

BACKGROUND OF THE INVENTION

Laser direct structuring processes (LDS) have been developed and usedfor the selective plating of molded plastic materials for more than 10years, so called molded interconnect devices (MID). With LDS it ispossible to realize highly functional circuit layouts on complex3-dimensional substrates. The basis of the process involves additivedoped thermoplastics or thermosets with inorganic fillers, which allowthe formation of circuit traces by means of laser activation, followedby metallization using electroless plating. The metal containingadditives incorporated in such plastics are activated by the laser beamand become active as a catalyst for electroless copper plating on thetreated areas of the surface of plastics to be plated. In addition toactivation, the laser treatment may create a microscopically roughsurface to which the copper becomes firmly anchored duringmetallization. However, such technology is limited to apply on additivedoped plastics, while general types of engineering plastic withoutadditive doping cannot be activated for electroless copper plating.

Another technology in use is proprietary paint together with LDS. It isdone by firstly spraying a thin layer of paint on the plastic parts. TheLDS process then creates the circuitry layout on the paint coating andin the meantime activates the paint on the circuitry. The plastic willthen go through electroless copper plating for metallization. Thisapproach can be extended to plastics without additive doping. However,it is still in prototype stages and not yet ready for mass production.

Laser restructuring printing (LRP) is another innovative technology forthe MID application. LRP employs high precision printing to createconductive diagrams (silver paste) on the workpiece to form the layoutof the circuit. The printed workpiece is then laser trimmed. A highprecision circuit structure is produced on the workpiece. Thistechnology involves higher start-up investment on costly 3D printingmachines.

Another technology is semi-additive process (SAP). The first step is toplate a thin layer of electroless copper on the plastic substratesemploying existing colloidal catalyst and electroless copper formetallization on printed circuit board. A layer of negativeelectrodeposited photoresist is coated on the plastic substrates. Uponexposure and development, the circuit pattern is exposed withoutcovering the photoresist. The exposed circuit can be plated with copperto achieve required thickness and then nickel. The remaining photoresistis removed. Excess copper layer is removed by micro-etch. An advantageof this technology is to be able to apply lower cost electrolyticplating processes for full copper build and nickel instead of the usualelectroless plating processes. The plastic substrate is already fullyplated with a layer of electroless copper. This technology can also beapplied on plastic without doping additives. However, since it does notinvolve using lasers to roughen the circuitry, plating adhesion is aconcern. In addition, the process sequence is quite long andcomplicated, with additional photoresist processes involved.

Although there are various processes relating to selective metallizationof polymer and plastic materials, there is still a need for an improvedmethod of selective metallization of polymers and plastics, inparticular MIDs.

SUMMARY OF THE INVENTION

A method of metallization of a polymer substrate including: providing apolymer substrate; applying a primer including a polyamine compound tothe polymer substrate to provide a hydrophilic coating on the polymersubstrate; applying a hydrophobic top coat directly adjacent the primerto form a shielding coating on the substrate, the hydrophobic top coatincludes one or more compounds chosen from alkyl alcohol alkoxylates,alkyl thiols, non-polymer primary alkyl amines and non-polymer secondaryalkyl amines; selectively etching the shielding coating to exposeportions of the polymer substrate; providing a catalyst to the polymersubstrate including the shielding coating; and selectively electrolessmetal plating the polymer substrate.

Shielding coatings may inhibit adsorption of catalysts on plasticsubstrates by their hydrophobic character which repels aqueous basedcatalysts or may deactivate adsorbed catalysts. In addition, theshielding coatings can inhibit background plating and overplating. Bothionic catalysts and colloidal catalysts can be used. Polymers with andwithout embedded catalysts can be used with the present invention. Themethods of the present invention can be used in the formation ofcircuitry on 3-D polymer substrates.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a schematic illustrating an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

As used throughout this specification, the abbreviations given belowhave the following meanings, unless the context clearly indicatesotherwise: g=gram; mg=milligram; mL=milliliter; L=liter; cm=centimeter;m=meter; mm=millimeter; μm=micron; ppm=parts per million; mg/L=ppm;M=molar; ° C.=degrees Centigrade; RT=room temperature; g/L=grams perliter; DI=deionized; MID=molded interconnect device; 3-D=three (3)dimensional; Pd=palladium; Nd:YAG=neodymium-doped yttrium aluminumgarnet; EO=ethylene oxide; PO=propylene oxide; PO-b-EO=propyleneoxide/ethylene oxide block copolymer; Mn=number average molecularweight; wt %=percent by weight; ABS=acrylonitrile-butadiene-styrenecopolymers; White ABS=white colored ABS; PC=polycarbonate polymer; BlackPC=black colored PC; GF=glass fiber; and T_(g)=glass transitiontemperature.

The term molded interconnect device or MID means an injection-moldedthermoplastic part with integrated electronic circuit traces whichtypically has a 3-D shape or form. The term “background plating” meansrandom metal deposition on a polymer or plastic surface where depositionof the metal is not intended. The term “overplating” means metal platingbeyond the desired circuit pattern and the inability to control themetal plating. The term “monomer” or “monomeric” means a single moleculewhich may combine with one or more of the same or similar molecules. Theterm “oligomer” means two or three monomers combined to form a singlemolecule. The term “polymer” means two or more monomers combined or twoor more oligomers combined to form a single molecule. The term “polymer”includes copolymers. The term “adjacent” means adjoining where twodifferent surfaces contact each other to form a common interface. Theterms “printed circuit board” and “printed wiring board” are usedinterchangeably throughout this specification. The terms “plating” and“deposition” are used interchangeably throughout this specification. Allamounts are percent by weight, unless otherwise noted. All numericalranges are inclusive and combinable in any order except where it islogical that such numerical ranges are constrained to add up to 100%.

The shielding coating of the present invention includes a primercomposition which includes one or more polyamines and is directlyapplied adjacent to a surface of a polymer or plastic material of asubstrate to provide a substantially hydrophilic coating on the polymeror plastic material followed by, without any intervening steps, exceptan optional rinse step, applying a hydrophobic top coat which includesone or more of alkyl alcohol alkoxylates, alkyl thiols, non-polymerprimary alkyl amines and non-polymer secondary alkyl amines directlyadjacent to the primer composition to form a shielding coating directlyadjacent to the polymer material of the substrate. Accordingly, theshielding coating includes the primer which includes the polyamine whichmay bind to the polymer by Van der Waals forces and the top coat whichincludes one or more of alkyl alcohol alkoxylates, alkyl thiols,non-polymer primary alkyl amines and non-polymer secondary alkyl amines.While not being bound by theory, it is believed that hydrophilicportions of the compounds which are included in the hydrophobic top coatinteract or intermix with the hydrophilic primer and the hydrophobicportions of the top coat compounds extend opposite to or away from thepolymer material of the substrate to form a substantially hydrophobictop surface thus forming the shielding coating layer on the polymersubstrate. The FIGURE illustrates the four basic steps of the presentinvention.

It is envisioned that any polyamine which can form a primer in theformation of the shielding coating of the present invention can be usedto practice the invention. Polyamines of the present invention areincluded in amounts of 0.5 g/L to 20 g/L, preferably 1 g/L to 15 g/L,more preferably from 1 g/L to 10 g/L. Preferably, polyamines are chosenfrom polyalkylene polyamines and linear and branched polyalkyleneimines(PAI).

Preferred polyalkylene polyamines have a general formula:

where R₁, R₂, R₃, R₄ and R₅ are independently chosen from hydrogen andlinear or branched (C₁-C₄)alkyl where a is from 2 to 6 and b is from 2to 6. Preferably R₁, R₂, R₃, R₄ and R₅ are independently chosen fromhydrogen and (C₁-C₂)alkyl and a is from 2 to 6 and b is from 2 to 6.More preferably R₁ and R₂ are hydrogen and R₃, R₄ and R₅ are chosen fromhydrogen and methyl and a is from 2 to 3 and b is from 2 to 6. Mostpreferably R₁, R₂, R₃, R₄ and R₅ are hydrogen and a is 2 and b is from 2to 6. Exemplary polyalkylene polyamines having formula (I) arediethylenetriamine, triethylenetetramine, tetraethylenepentamine,pentaethylenehexamine and hexaethyleneheptamine.

Preferred polyalkyleneimines (PAIs) of the present invention have ageneral formula:

H—(CH₂—(CH₂)_(d)—NH—)_(e)—H  (II)

where d and e are the same or different and are at least 1. Preferably dis 1 to 4 and e is a value greater than 25. More preferably e is greaterthan 250 and most preferably e is greater than 2500. The most preferredmolecular weight (Mn) is 800 and greater, more preferably from 1500 andgreater and most preferably from 2500 and greater.

More preferred polyalkyleneimines (PAIs) are polyethyleneimines (PEIs).Such PEIs are believed to have the following general formula though itis not known for certain within the industry:

—(NHCH₂CH₂-)_(f)[—N(CH₂CH₂NH₂)CH₂CH₂-]_(g)  (III)

where f is from 1 to 120,000, preferably from 2 to 60,000, morepreferably from 3 to 24,000 and g is from 1 to 60,000, preferably from 2to 30,000, more preferably from 3 to 12,000. Exemplarypolyethyleneimines of formula (III) are PEI-3, PEI-7, PEI-15, PEI-30,PEI-45, PEI-100, PEI-300, PEI-500, PEI-600, PEI-700, PEI-800, PEI-1000,PEI-1500, PEI-1800, PEI-2000, PEI-70,000, PEI-500,000 and PEI-5,000,000,where the integer refers to the molecular weight of the polymer. PEIswhich are designated as such are available from Aldrich.

Polyethyleneimines (PEIs) of the present invention also include branchedprotonated polyethyleneimines (PEI salts). In branched protonatedpolyethyleneimines (PEI salts) a counterion of each protonated nitrogencenter is balanced with an anion of an acid obtained duringneutralization. Examples of branched protonated polyethyleneimines arePEI-hydrochloride salt, PEI-sulfuric acid salt, PEI-nitric acid salt,PEI-acetic acid salt, and PEI-fatty acid salt.

Optionally, the primer composition can include one or more metal ions toassist the mixing of the primer with the top coat compounds. Such metalions include, but are not limited to copper ions, nickel ions, manganeseions and zinc ions. Such ions are added to the primer composition bytheir water soluble salts. Copper salts include but are not limited tocopper sulfate, copper nitrate, copper chloride and copper acetate.Nickel salts include, but are not limited to nickel chloride, nickelsulfate and nickel sulfamate. Manganese salts include, but are notlimited to manganese sulfate. Zinc salts include, but are not limited tozinc nitrate. Such salts are included in the primer in amounts of 0.5g/L to 15 g/L, preferably from 1 g/L to 10 g/L. Preferably the metalions of choice are copper and nickel. More preferably the ions of choiceare copper ions. In general, it is preferred to include one or moremetal ions in the primer solution; however, minor experimentation can bedone to determine whether or not the one or more metal ions improveadsorption of the topcoat compounds to a particular polymer material.

The primer can be prepared by mixing the components in any order inwater. A pH of the primer can range preferably from 7 to 13, morepreferably from 8 to 12.

Prior to applying the primer to the polymer material, it is preferredthat the polymer material is cleaned to remove any surface oils andresidue from the surface of the polymer. The FIGURE illustrates acleaned substrate at step 1. Conventional cleaning compositions andmethods known in the art can be used. Typically cleaning is done at roomtemperature in a cleaning solution such as 10% CUPOSIT™ Z cleaningformulation (available from Dow Advanced Materials, Marlborough, Mass.)using ultrasound.

The primer can be applied directly adjacent the polymer material byimmersing the substrate containing the polymer material in the primer orit can be sprayed directly adjacent to the polymer material. Preferablythe primer is applied at temperatures from room temperature to 80° C.,more preferably from 30° C. to 50° C. Dwell times prior to contact ofthe polymer material with the top coat range from preferably 1 minute to10 minutes, more preferably from 3 minutes to 8 minutes.

After application of the primer to the polymer material of thesubstrate, the top coat is applied directly adjacent to the primer onthe polymer material without any intervening steps in the method of thepresent invention except for an optional water rinse step. The top coatis applied directly adjacent to the primer by immersing the polymermaterial in a solution of the top coat or by spraying the top coatdirectly adjacent the primer coating the polymer material. The top coatis preferably applied at a temperature from room temperature to 80° C.,more preferably from 30° C. to 50° C. Dwell times for the application ofthe top coat range from preferably 1 minute to 10 minutes, morepreferably from 3 minutes to 8 minutes. After the top coat is applied tothe primer, the top coat is allowed to dry on the primer to form theshielding coating directly adjacent to the polymer material in thesubstrate. The FIGURE illustrates the shielding coating adjacent thepolymer substrate. Optionally, the top coat can be dried by blow dryingat room temperature.

Top coats are chosen from alkyl alcohol alkoxylates, alkyl thiols andnon-polymer primary and non-polymer secondary amines. They can beincluded in amounts of 0.5 g/L to 100 g/L, preferably from 1 g/L to 30g/L. Alkyl alcohol alkoxylates include, but are not limited topolyethoxylated alcohol polymers having formula:

CH₃(CH₂)_(m)—(O—CH₂—CH₂)_(n)—OH  (IV)

where m is 7 to 25; and n represents an average degree of ethoxylationfrom 1 to 25. Preferably n is 7 to 15 and m is preferably from 13 to 25.Alkyl alcohol alkoxylates also include aliphaticethoxylated/propoxylated copolymers having a formula:

R—O—(CH₂CH₂O)_(x)—(CH₂CH₂CH₂O)_(y)—H  (V) or

R—O—(CH₂CH₂O)_(x)—(CH₂CH(CH₃)O)_(y)—H  (VI)

where R is a linear or branched chain alkyl group having 8 to 22 carbonatoms or an isotridecyl group and x and y are independently chosen from1 to 20. Alkyl alcohol alkoxyaltes also include propoxylated/ethoxylatedcopolymers having a formula:

R—O—(CH₂CH(CH₃)O)_(x)—(CH₂CH₂O)_(y)—H  (VII) or

R—O—(CH₂CH₂CH₂O)_(x)—(CH₂CH₂O)_(y)—H  (VIII)

where R and x and y are defined as above.

Alkyl thiols include, but are not limited to thiols having a formula:

R₆—SH  (IX)

where R₆ is a linear or branched alkyl group having from 1 to 24 carbonatoms, preferably, from 16 to 21 carbon atoms, an aryl group having from5 to 14 carbon atoms and an alkylaryl where the alky of the alkylaryl islinear or branched with 1 to 24 carbon atoms and the aryl has from 5 to14 carbon atoms. Exemplary alkyl thiols are ethanethiol, 1-propanethiol,2-propanethiol, 1-butanethiol, 2-butanethiol, 2-methyl-1-propanethiol,2-methyl-2-propanethiol, 2-methyl-1-butanethiol, 1-pentanethiol,2,2-dimethyl-1-propanethiol, 1-hexanethiol, 1,6-hexanethiol,1-heptanethiol, 2-ethylhexanethiol, 1-octanethiol, 1,8-octanethiol,1-nonanethiol, 1,9-nonanethiol, 1-decanethiol, 1-undecanethiol,1-dodecanthiol, 1-tridecanethiol, 1-tetradecanethiol,1-pentadecanethiol, 1-hexadecanethiol, 1-heptadecanethiol,1-octadecanethiol, 1-nonadecanthiol and 1-eicosanethiol. Preferredexemplary alky thiols are 1-hexadecanethiol, 1-heptadecanethiol,1-octadecanethiol, 1-nonadecanthiol and 1-eicosanethiol.

Non-polymer primary and non-polymer secondary amines include, but arenot limited to amine compounds having a formula:

R₇—CH₂—NH₂  (X) or

R₈—CH₂—NH—CH₂—R₉  (XI)

where R₇, R₈ and R₉ are independently chosen from hydrogen, linear orbranched, substituted or unsubstituted (C₁-C₂₄)alkyl, linear orbranched, substituted or unsubstituted (C₂-C₂₀)alkenyl, substituted orunsubstituted (C₃-C₈)cycloalkyl and substituted or unsubstituted(C₆-C₁₀)aryl where substituent groups include, but are not limited tohydroxyl, hydroxy(C₁-C₂₀)alkyl, amino, (C₁-C₂₀)alkoxy, halogen such asfluorine, chlorine and bromine, mercapto and phenyl. Preferably theamine compound is a non-polymer primary amine where R₇ is a linear orbranched, substituted or unsubstituted (C₁-C₂₁)alkyl, more preferably,the amine compound is a non-polymer primary amine where R₇ is a linearor branched, unsubstituted (C₁-C₂₁)alkyl.

Exemplary primary amines include aminoethane, 1-aminopropane,2-aminopropane, 1-aminobutane, 2-aminobutane,1-amino-2-methylaminopentane, 2-amino-2-methylpropane, 1-aminopentane,2-aminopentane, 3-aminopentane, neo-pentylamine, 1-aminohexane,1-aminoheptane, 2-aminoheptane, 1-aminooctane, 2-aminoocatne,1-aminononane, 1-aminodecane, 1-aminododecane, 1-aminotridecane,1-aminotetradecane, 1-aminopentadecane, 1-aminohexadecane,1-aminoheptadecane and 1-aminoocatdecane. Preferably the exemplaryprimary amines include 1-aminohexadecane, 1-aminoheptadecane and1-aminoocatdecane.

Optionally, the topcoat can include one or more organic solvents toassist in solubilizing the organic compounds. Organic solvents areincluded in amounts sufficient to solubilize the hydrophobic topcoatcompounds. Preferably the one or more organic solvents are included inamounts of 0-60% by volume, preferably 10% by volume to 50% by volume.Such organic solvents include alcohols, diols, triols, and higherpolyols. Suitable alcohols include ethanol, propanol, isopropanol,n-butanol, isobutanol, tert-butanol, ethylene glycol, propane-1,2-diol,butane-1,2-diol, butane-1,3-diol, butane-1,4-diol, propane-1,3-diol,hexane-1,4-diol, hexane-1,5-diol, hecane-1,6-diol, 2-methoxyethanol,2-ethoxyethanol, 2-propaoxyethanol and 2-butoxyeethanol. Also includedare unsaturated diols, such as butane-diol, hexane-diol and acetylenicssuch as butyne diol. A suitable triol is glycerol. Additional alcoholsinclude triethylene glycol, diethylene glycol, diethylene glycol methylether, tirethylene glycol monomethyl ether, triethylene glycol dimethylether, propylene glycol, diprolylene glycol, allyl alcohol, furfurylalcohol, tetrahydrofurfurly alcohol and block polymers of polyethyleneand polyethylene glycol.

After the shielding coating is formed on the polymer material of thesubstrate, the shielding coating is selectively etched to form a patternfor electrical circuitry. The pattern may be etched by conventionalmethods known in the plating on plastics industry such as, but notlimited to, laser etching, sand paper etching and plasma etching.Preferably, the shielding coating is selectively etched with a laserlight such as a Nd:YAG, 1064 nm LPKF Laser available from LPKF Laser &Electronics AG. Laser etching enables the formation of fine linepatterns for fine line circuitry since the laser light can be adjustedto a very fine dimension. This further enables the miniaturization ofcircuitry and for the miniaturization of 3-D electronic articles.Typical track widths are greater than or equal to 150 μm and spacing orgaps of greater than or equal to 200 μm. Etching is done to remove theshielding coating down to the polymer material and to roughen thepolymer surface as illustrated in the FIGURE at step 3. If the polymermaterial has an embedded catalyst, sufficient polymer material at thesurface is removed to expose the catalyst for electroless metal plating.If the polymer material does not include an embedded catalyst, aconventional ionic catalyst or colloidal catalyst can be applied to thepolymer for electroless metal plating as illustrated in step 4 of theFIGURE. The ionic or colloidal catalyst can be applied by conventionalmeans such as by dipping or spraying the catalyst on the etchedsubstrate. Conventional catalyst parameters such as temperature, pH anddwell times of catalyst solutions can be used to practice the presentinvention. Depending on the type of catalyst conventionalpost-treatments may be used to activate the catalyst before electrolessmetallization. Ionic catalysts preferably include catalytic ions such assilver ions and palladium ions. Typically complexing agents are includewith the metal ions to stabilize them prior to catalysis. Colloidalcatalysts are preferably the conventional tin/palladium.

If the catalyst is an ionic catalyst, following application of thecatalyst to the polymer and prior to metallization one or more reducingagents are applied to the catalyzed polymer to reduce the metal ions totheir metallic state. Conventional reducing agents known to reduce metalions to metal may be used. Such reducing agents include, but are notlimited to dimethylamine borane, sodium borohydride, ascorbic acid,iso-ascorbic acid, sodium hypophosphite, hydrazine hydrate, formic acidand formaldehyde. Reducing agents are included in amounts to reducesubstantially all of the metal ions to metal. Such amounts are generallyconventional amounts and are well known by those of skill in the art.

The method of the present invention can be used to electroless metalplate various substrates such as printed circuit boards and MIDs.Preferably, the method of the present invention is used to selectivelyelectroless metal plate MIDs which typically have a 3-D configuration,not the planar configuration of substrates such as printed circuitboards. Such 3-D configured substrates are difficult to electrolessmetal plate with continuous and uniform circuits because of their 3-Dconfigurations where circuits are required to follow the irregularcontours of the surface of the MID configuration. Such printed circuitboards and MIDs can include polymer materials of thermosetting resins,thermoplastic resins and combinations thereof, including fiber, such asfiberglass, and impregnated embodiments of the foregoing.

Thermoplastic resins include, but are not limited to acetal resins,acrylics, such as methyl acrylate, cellulosic resins, such as ethylacetate, cellulose propionate, cellulose acetate butyrate and cellulosenitrate, polyethers, nylon, polyethylene, polystyrene, styrene blends,such as acrylonitrile styrene and copolymers and acrylonitrile-butadienestyrene copolymers, polycarbonates, polychlorotrifluoroethylene, andvinylpolymers and copolymers, such as vinyl acetate, vinyl alcohol,vinyl butyral, vinyl chloride, vinyl chloride-acetate copolymer,vinylidene chloride and vinyl formal.

Thermosetting resins include, but are not limited to allyl phthalate,furane, melamine-formaldehyde, phenol-formaldehyde and phenol-furfuralcopolymers, alone or compounded with butadiene acrylonitrile copolymersor acrylonitrile-butadiene-styrene copolymers, polyacrylic esters,silicones, urea formaldehydes, epoxy resins, allyl resins, glycerylphthalates and polyesters.

The methods of the present invention can be used to plate substrateswith both low and high T_(g) resins. Low T_(g) resins have a T_(g) below160° C. and high T_(g) resins have a T_(g) of 160° C. and above.Typically high T_(g) resins have a T_(g) of 160° C. to 280° C. or suchas from 170° C. to 240° C. High T_(g) polymer resins include, but arenot limited to, polytetrafluoroethylene (PTFE) andpolytetrafluoroethylene blends. Such blends include, for example, PTFEwith polypheneylene oxides and cyanate esters. Other classes of polymerresins which include resins with a high Tg include, but are not limitedto, epoxy resins, such as difunctional and multifunctional epoxy resins,bimaleimide/triazine and epoxy resins (BT epoxy), epoxy/polyphenyleneoxide resins, acrylonitrile butadienestyrene, polycarbonates (PC),polyphenylene oxides (PPO), polypheneylene ethers (PPE), polyphenylenesulfides (PPS), polysulfones (PS), polyamides, polyesters such aspolyethyleneterephthalate (PET) and polybutyleneterephthalate (PBT),polyetherketones (PEEK), liquid crystal polymers, polyurethanes,polyetherimides, epoxies and composites thereof.

While it is envisioned that the present invention can be used toelectroless deposit any metal which may be electroless plated,preferably, the metal is chosen from copper, copper alloys, nickel ornickel alloys. An example of a commercially available electroless copperplating bath is CIRCUPOSIT™ 880 Electroless Copper bath (available fromDow Advanced Materials, Marlborough, Mass.). Another example of acommercially available electroless nickel plating bath is DURAPOSIT™ SMT88 (available from Dow Advanced Materials, Marlborough, Mass.). Anexample of a commercially available electroless nickel bath isDURAPOSIT™ SMT 88 electroless nickel (available from Dow AdvancedMaterials, Marlborough, Mass.).

Typically sources of copper ions include, but are not limited to watersoluble halides, nitrates, acetates, sulfates and other organic andinorganic salts of copper. Mixtures of one or more of such copper saltsmay be used to provide copper ions. Examples include copper sulfate,such as copper sulfate pentahydrate, copper chloride, copper nitrate,copper hydroxide and copper sulfamate. Conventional amounts of coppersalts can be used in the compositions.

One or more alloying metals also can be included in the electrolesscompositions. Such alloying metals include, but are not limited tonickel and tin. Examples of copper alloys include copper/nickel andcopper/tin. Typically the copper alloy is copper/nickel.

Sources of nickel ions for nickel and nickel alloy electroless baths caninclude one or more conventional water soluble salts of nickel. Sourcesof nickel ions include, but are not limited to, nickel sulfates andnickel halides. Sources of nickel ions can be included in theelectroless alloying compositions in conventional amounts. Sources oftin ions include, but are not limited to tin sulfates, tin chloride andorganic tin salts such as tin alkyl sulfonates. Tin salts can beincluded in the electroless alloying compositions in conventionalamounts.

Electroless metal plating parameters, such as temperature and time canbe conventional and are well known in the art. The pH of the electrolessmetal plating bath is typically alkaline.

During selective electroless metal plating of the exposed polymermaterial the portions of the polymer material coated with the shieldingcoating inhibit electroless metal plating as illustrated in step 5 ofthe FIGURE. Undesired background plating and overplating on portions ofthe polymer coated with the shielding coating are inhibited such thatmetal plating occurs substantially in the etched portions of thepolymer. The shielding coating enables the formation of metal circuitrywhich follows the contours of a 3-D article while inhibiting backgroundplating and overplating which can result in defective articles. Thecombination of the laser etching which enables fine line circuitpatterning and the shielding coating enable the formation of continuousminiaturized circuits on the irregular surface of 3-D polymer substratesfor the formation of miniaturized electronic articles.

The following examples are not intended to limit the scope of theinvention but to further illustrate the invention.

Example 1

A plurality of polymer substrates was provided. Each substrate wastreated and selectively electroless copper plated according to themethod disclosed in Table 1 below. Most of the substrates had embeddedcatalysts of spinel heavy metal oxides or heavy metal complexes.Portions of the shielding coating where electroless copper plating wasto take place were removed with silicon carbide type, P220 sandpaper. Ifthe substrate did not have an embedded catalyst, an aqueous ioniccatalyst was applied to the substrate prior to electroless plating. Theaqueous ionic catalyst solution included 200 ppm palladium ions and1,020 ppm 2,6-dimethylpyrazine. The reducing agent was dimethylamineborane at a concentration of 1 g/L. Electroless copper plating was donewith CUPOSIT™ 71HS electroless copper bath available from Dow AdvancedMaterials.

TABLE 1 Process Step Component and Conditions Cleaning Ultrasoniccleaning with 10% CUPOSIT ™ Z at RT for 30 seconds Primer 0.03M (5.68g/L) tetraethylenepentamine, 0.045M (6.05 g/L) copper chloride at 40° C.for 5 minutes, pH = 10 Top Coat 5 g/L polyethylene-block-poly(ethyleneglycol) Mn ~1400, 30 mL/L (30 g/L) No Tarn PM-3 (1-octadecanethiol 10wt/wt % and C₁₃H₂₇—(OC₂H₄)_(n)OH, where n is from 3 to 20, 85 wt/wt %),500 mL/L propylene glycol at 40° C. for 5 minutes. Selective removalSandpaper rubbing of shielding coating Catalyst Ionic catalyst at 40° C.for 5 minutes followed by dimethylamine borane at pH = 5 for 1 minute.Electroless copper CUPOSIT ™ 71HS at 56° C. for 15 minutes

TABLE 2 Polymer Trade Name Embedded Catalyst Transparent acrylic — NoWhite ABS — No White PC/ABS XANTAR ™ C CP200 No Black PC/ABS 30% GFLAG ™ 2930 No White PC/ABS XANTAR ™ 3724 Yes White PC/ABS XANTAR ™ 3734Yes Black PC XANTAR ™ 3760 Yes Black PC/PET XANTAR ™ 3780 Yes Black PCXANTAR ™ 4700 Yes Black PC/ABS H.W. TPJH231F Yes White PC/ABS SABIC ™ NX11302 Yes Black polyamide RENY ™ XHP 1002 Yes Black polyamide RENY ™ XHP1003 Yes Black polyamide RENY ™ XHP 2081 Yes

After each polymer substrate was electroless copper plated, thesubstrates were rinsed with DI water at room temperature and analyzedfor the quality of the copper deposits. All of the copper depositsappeared uniform and bright. No background plating or overplating wasobserved on any of the substrates.

Example 2

A plurality of white ABS and a black PC (XANTAR™ 3730) polymersubstrates were selectively electroless plated with copper according tothe method disclosed in Table 3 below.

TABLE 3 Process Step Component and Conditions Cleaning Ultrasoniccleaning with 10% CUPOSIT ™ Z at RT for 30 seconds Primer 0.03M (5.68g/L) tetraethylenepentamine, 0-0.06M (0-8.07 g/L) copper chloride at 40°C., pH = 9-10 for 5 minutes Top Coat 30 mL/L (30 g/L) No Tarn PM-3(1-octadecanethiol 10 wt/wt % and C₁₃H₂₇—(OC₂H₄)_(n)OH, where n is from 3to 20, 85 wt/wt %), 500 mL/L propylene glycol at 40° C. for 5 minutes.Selective removal Sandpaper rubbing of shielding coating Catalyst Ioniccatalyst as described in Example 1 at 40° C. for 5 minutes followed bydimethylamine borane at pH = 5 for 1 minute. Electroless copperCUPOSIT ™ 71HS at 56° C. for 15 minutes

The polymer substrates were analyzed for the quality of the copperdeposit and also for any background plating. All of the copper depositsappeared bright and smooth. Table 4 below discloses the results relatingto background plating and the concentration of copper chloride in theprimer composition.

TABLE 4 Copper Chloride Background Plating Background PlatingConcentration on White ABS on Black PC 0M (0 g/L) No Minor (<5% byvisual inspection) 0.015M (2.02 g/L)  No No 0.03M (4.04 g/L) No No0.045M (6.06 g/L)  No No 0.06M (8.07 g/L) No No

With the exception of minor background plating of the black PC where thecopper chloride was not included in the primer containingtetraethylenepentamine, all of the polymer samples appeared free of anybackground plating.

Example 3

A white ABS and a black PC (XANTAR™ 3730) were selectively electrolessplated according to the method disclosed in Table 5 below.

TABLE 5 Process Step Component and Conditions Cleaning Ultrasoniccleaning with 10% CUPOSIT ™ Z at RT for 30 seconds Primer 5.2 g/Lpolyethyleneimine (Mn = 600,000- 1,000,000) 50% w/v aqueous solutionfrom Aldrich Chemicals, 0-0.06M (0-8.07 g/L) copper chloride at 40° C.,pH = 9-10, for 5 minutes Top Coat 30 mL/L (30 g/L) No Tarn PM-3(1-octadecanethiol 10 wt/wt % and C₁₃H₂₇—(OC₂H₄)_(n)OH, where n is from 3to 20, 85 wt/wt %), 500 mL/L propylene glycol at 40° C. for 5 minutes.Selective removal Sandpaper rubbing of shielding coating Catalyst Ioniccatalyst as described in Example 1 at 40° C. for 5 minutes followed bydimethylamine borane at pH = 5 for 1 minute. Electroless copperCUPOSIT ™ 71HS at 56° C. for 15 minutes

The polymer substrates were analyzed for the quality of the copperdeposit and also for any background plating. All of the copper depositsappeared bright and smooth. Table 6 below discloses the results relatingto background plating and the concentration of copper chloride in theprimer composition.

TABLE 6 Copper Chloride Background Plating Background PlatingConcentration on White ABS on Black PC 0M (0 g/L) Yes (100% of polymerYes (100% of polymer surface was covered surface was covered withcopper) with copper) 0.015M (2.02 g/L)  Minor (<5%) Minor (<5%) 0.03M(4.04 g/L) Minor (~10%) Minor (<5%) 0.045M (6.06 g/L)  No No 0.06M (8.07g/L) No No

Although there was minor background plating where the concentration forcopper chloride concentrations of 0.015 M and 0.03 M, the addition ofcopper chloride significantly inhibited background plating when theprimer composition included polyethyleneimine.

What is claimed is:
 1. A method of metallization of a polymer substratecomprising: a) providing a polymer substrate; b) applying a primercomprising a polyamine compound to the polymer substrate to provide ahydrophilic coating on the polymer substrate; c) applying a hydrophobictop coat directly adjacent the primer to form a shielding coating on thesubstrate, the hydrophobic top coat comprises one or more compoundschosen from alkyl alcohol alkoxylates, alkyl thiols, non-polymer primaryalkyl amines and non-polymer secondary alkylamines; d) selectivelyetching the shielding coating to expose portions of the polymersubstrate; e) providing a catalyst to the polymer substrate comprisingthe shielding coating; and f) selectively electroless metal plating thepolymer substrate.
 2. The method of claim 1, wherein the polyamine ischosen from polyalkylene polyamines and linear or branchedpolyalkyleneimines.
 3. The method of claim 2, wherein the polyalkylenepolyamines have a general formula:

where R₁, R₂, R₃, R₄ and R₅ are independently chosen from hydrogen andlinear or branched (C₁-C₄)alkyl where a is from 2 to 6 and b is from 2to
 6. 4. The method of claim 3, wherein the polyalkylene polyamines arechosen from diethylenetriamine, triethylenetetramine,tetraethylenepentamine, pentaethylenehexamine and hexaethyleneheptamine.5. The method of claim 2, wherein the linear polyalkyleneimines have aformula:H—(CH₂—(CH₂)_(d)—NH—)_(e)—H  (II) where d and e are the same ordifferent and are at least
 1. 6. The method of claim 2, wherein thelinear or branched polyalkyleneimines have a formula:—(NHCH₂CH₂-)_(f)[—N(CH₂CH₂NH₂)CH₂CH₂-]_(g)  (III) where f is from 1 to120,000 and g is from 1 to 60,000.
 7. The method of claim 2, wherein thebranched polyalkyleneimines are protonated polyethyleneimines (PEIsalts).
 8. The method of claim 1, wherein the alkyl alcohol alkoxylatesare polyethoxylated alcohol polymers having a formula:CH₃(CH₂)_(m)—(O—CH₂—CH₂)_(n)—OH  (IV) where m is 7 to 25; and nrepresents an average degree of ethoxylation from 1 to
 25. 9. The methodof claim 1, wherein the alkyl alcohol alkoxylates are aliphaticethoxylated/propoxylated copolymers having a formula:R—O—(CH₂CH₂O)_(x)—(CH₂CH₂CH₂O)_(y)—H  (V) orR—O—(CH₂CH₂O)_(x)—(CH₂CH(CH₃)O)_(y)—H  (VI) where R is a linear orbranched chain alkyl group having 8 to 22 carbon atoms or an isotridecylgroup and x and y are independently chosen from 1 to
 20. 10. The methodof claim 1, wherein the alkyl alcohol alkoxylates are aliphaticpropoxylated/ethoxylated copolymers having the following formula:R—O—(CH₂CH(CH₃)O)_(x)—(CH₂CH₂O)_(y)—H  (VII) orR—O—(CH₂CH₂CH₂O)_(x)—(CH₂CH₂O)_(y)—H  (VIII) where R is a linear orbranched chain alkyl group having 8 to 22 carbon atoms or an isotridecylgroup and x and y are independently chosen from 1 to
 20. 11. The methodof claim 1, wherein the alkyl thiols have a formula:R₆—SH  (IX) wherein R₆ is a linear or branched alkyl group having from 1to 24 carbon atoms, an aryl group having from 5 to 14 carbon atoms or analkylaryl, wherein the alky of the alkylaryl is linear or branched with1 to 24 carbon atoms and the aryl has from 5 to 14 carbon atoms.
 12. Themethod of claim 1, wherein the non-polymer primary amines have aformula:R₇—CH₂—NH₂  (X) wherein R₇, are independently chosen from hydrogen,linear or branched, substituted or unsubstituted (C₁-C₂₀)alkyl, linearor branched, substituted or unsubstituted (C₂-C₂₀)alkenyl, substitutedor unsubstituted (C₃-C₈)cycloalkyl or substituted or unsubstituted(C₆-C₁₀)aryl.
 13. The method of claim 1, wherein the non-polymersecondary amines have a formula:R₈—CH₂—NH—CH₂—R₉  (XI) wherein R₈ and R₉, are independently chosen fromhydrogen, linear or branched, substituted or unsubstituted(C₁-C₂₀)alkyl, linear or branched, substituted or unsubstituted(C₂-C₂₀)alkenyl, substituted or unsubstituted (C₃-C₈)cycloalkyl orsubstituted or unsubstituted (C₆-C₁₀)aryl.
 14. The method of claim 1,wherein the primer further comprises one or more metal ions.
 15. Themethod of claim 14, wherein the one or more metal ions are chosen fromcopper, nickel, manganese and zinc.
 16. The method of claim 1, whereinthe hydrophobic top coat further comprises one or more organic solvents.17. The method of claim 16, wherein the one or more organic solvents arechosen from alcohols, diols, triols and higher polyols.
 18. The methodof claim 1, wherein a metal is copper.